This invention relates generally to a chain tensioner for chain drives which is particularly, though not exclusively, suitable for use as a tensioner on the timing chain of a motor vehicle engine. The present invention is a chain tensioner particularly suited for use in confined spaces having a flat blade spring element mechanically interlocked with a plastic shoe. The shoe may be of rigid filled nylon and engages the chain to be tensioned.
Conventionally, a blade tensioner is used as the tensioner to apply tension force onto a chain. One form of blade chain tensioner is shown in U. S. Pat. No. 3,490,302, which is incorporated herein by reference. Another example of a prior art blade tensioner is shown in FIGS. 9-11 herein.
As shown in FIG. 9, the conventional blade tensioner 100 is composed of a shoe 101 made of resin that extends in an arcuate form. Multiple blade springs 102 extend along shoe 101 and are mounted on shoe 101. A metal base or plate 120 supports shoe 101. A first projecting portion 110, having a curved surface 110a is formed at the tip or free end of shoe 101. A concave opening or groove 111, for housing one end of blade spring 102, is formed in the projecting portion 110 and shoe 101. A triangular projecting portion 112 is formed on the fixed end of shoe 101. A concave opening or groove 113, for housing the other end of blade spring 102, is formed in the projecting portion 112 and shoe 101.
Attachment holes 121, 122 are formed on base 120. A sliding surface 125 is formed at the tip of base 120 so that projecting part 110, at the tip or free end of the shoe 101 can slide on it while in contact. As shown in FIG. 10, projecting portion 112, on the fixed end of shoe 101 and one end of metal pin 130, is fixed at the center of plate 120 and, on the other hand, a through hole 112a, formed in pin 130, is inserted in the through hole 112a. Stopper ring 131, for shoe 101, is mounted on the tip of pin 130. With this composition, shoe 101 is rotatable ground pin 130. A chain (not shown) runs on sliding surface 101a of shoe 101. When the chain is in operation, a pressure load acts on the chain via shoe 101, as shown in FIG. 11, when the spring 102 deforms.
Not only the chain, but also the tensioner is exposed to wide-ranging temperature fluctuation in an automotive application. Therefore, the components of the tensioner repeat thermal expansion and thermal contraction during automobile operation.
However, in a conventional blade tensioner, the resin shoe is supported by a metal pin and the coefficients of thermal expansion of these components differ greatly from one another. Therefore, the difference occurs in the magnitude of thermal deformation of the shoe and pin and, as a result, smooth rotation of the shoe around the pin is hindered when there are high temperature fluctuations. In this case, the shape of the groove for housing the spring end on the fixed end of the shoe deforms and the operation of the spring can be adversely affected, thereby the blade tensioner response deteriorates.
This invention addresses such conventional problems and offers a blade tensioner that provides reduced deterioration of tensioner response and improves durability.
The blade tensioner of one embodiment of the present invention includes a blade tensioner that applies tension force to a chain. The blade tensioner has a base or bracket and a chain sliding or contacting surface over which the chain slides. The chain-contacting surface is a surface portion of a resin or plastic shoe having an arcuate shape. The shoe is made of a plastic material which will xe2x80x9ccreep.xe2x80x9d xe2x80x9cCreepxe2x80x9d is the term used in the art to describe the tendency of the shoe to plastically deform in a gradual manner under elevated load and temperature. The fixed or proximal end of the shoe is rotatably mounted to a pin. The pin is formed of metal, preferably steel or aluminum. The pin is fixed to the base. The free end or distal part of the shoe slides freely on an adjacent sliding surface formed on the base. A flat blade spring or multiple blade springs are positioned on the side of the shoe opposite the chain-contacting surface of the shoe. The springs have ends inserted into grooves, slots or housings formed in the opposite ends of the shoe. A bushing is press-fit into a bore formed in the fixed end of the shoe and the pin is inserted rotatably into the bushing. The bushing is made of metal, preferably steel or aluminum, and more preferably being of the same metal as the pin. The bushing is press-fit on the fixed end of the blade shoe. Both the bushing and the pin are made of metal.
Therefore, different from a conventional blade tensioner, the difference in magnitude of thermal deformation of the bushing and pin is small, even with large temperature fluctuations, so that the clearance between these two components can be maintained at a nearly constant value. Thereby, the shoe can rotate smoothly around the pin and, as a result, deterioration of response due to temperature fluctuation can be reduced.
The blade tensioner of a second embodiment includes a blade tensioner that applies tension force to a chain. The blade tensioner has a base or bracket and a chain sliding or contacting surface over which the chain slides. The chain-contacting surface is a surface portion of a resin or plastic shoe. The fixed or proximal end of the shoe is rotatably mounted to a metal pin. The pin is fixed to the base. The free end or distal part of the shoe slides freely on an adjacent sliding surface formed on the base. A flat blade spring or multiple blade springs are positioned on the side of the shoe opposite the chain-contacting surface of the shoe. The springs have ends inserted into grooves, slots or housings formed in the opposite ends of the shoe. A metal bushing is press-fit into a bore formed in the fixed end of the shoe and the pin is inserted rotatably into the bushing. The blade spring end adjacent the fixed end of the shoe is inserted between the bushing and the face of the shoe opposite the chain-contacting surface. The bushing may be any suitable shape in cross-section. Preferably, the cross-section of the bushing is circular or polygonal. The end of the blade spring adjacent the fixed end of the shoe is inserted between the bushing and the blade shoe.
Therefore defective operation of the blade spring due to thermal deformation of the groove or concave part for housing the blade spring which is formed in the fixed end of the shoe does not occur as in the conventional blade tensioner. Thereby, deterioration of response of the blade tensioner is reduced.
The blade tensioner of a third embodiment of the present invention has a shoe provided with an arcuate form mounted to a base. The shoe has a chain sliding surface on which the chain slides. The fixed end of the shoe is provided rotatable around a metal pin that is fixed to the base. A free end of the shoe opposite the fixed end is provided to slide on the sliding surface formed in the base. A blade spring is mounted on the surface of the shoe that is opposite the chain sliding surface of the shoe. A projecting portion is formed at the widthwise center of the blade spring mounting surface of the shoe adjacent the fixed end of the shoe. A stepped bushing made of metal with a center portion having a relatively small diameter is press-fit into a through hole formed in the projecting portion. Large diameter elements, flanges or portions are provided on both ends of the bushing. A cut-out into which the projecting portion of the shoe is inserted is formed in the blade spring adjacent the fixed end of the shoe, and the spring end is inserted in a gap between the large diameter portion of the bushing and the shoe.
The bushing can have either a circular or polygonal cross-section. When it is circular, the contact point of the blade spring with the circular surface of the bushing acts as a pivot for applying the load. When it is polygonal, such as triangular, etc., the contact area of the blade spring (i.e., pressure-bearing area) with the bushing can be made larger when the contact point between blade spring and any one surface of the bushing can be used as a pivot for applying the load, thereby surface pressure and the resulting wear can be reduced. In such case, the span of the blade spring can be maintained at a constant value, so that the loading property of the blade spring can be made linear for easier loading control.
The blade tensioner of a fourth embodiment of the present invention has a large diameter bushing, the cross-section of which is circular or polygonal.
A projecting portion is formed at the widthwise center of the blade spring mounting surface on the shoe fixed end. A small diameter stepped bushing made of metal is press-fit into the through hole in the projecting portion and the pin is supported rotatably in the bushing. Thereby, similarly to the first embodiment of the invention, the shoe rotates smoothly around the pin regardless of temperature, and, as a result, deterioration of the response due to temperature fluctuation can be reduced.
Large diameters elements or portions are formed at both ends of the bushing and a cut-out for insertion of the projecting portion is formed in the blade spring end adjacent the fixed end of the shoe. The spring end adjacent the fixed end of the shoe is inserted in the gap between the large diameter bushing and the shoe and held in place by the bushing. Thereby, similar the second embodiment of the present invention, defective operation of the blade spring and deterioration of response of the blade tensioner can be reduced.
In a fifth embodiment of the invention, a cross-section of the large diameter part of the bushing is circular or polygonal. Therefore, similar to the third embodiment of the present invention, the contact point of the blade spring with the circular surface of the large diameter part of the bushing acts as a load applying pivot when the cross-section is circular.
When the cross-section is polygonal, the area of contact with the blade spring (i.e., pressure bearing area) can be made larger by using the contact point between the blade spring and either surface of the large diameter part of the bushing as a load applying pivot and thereby the surface pressure can be reduced. In this case, the loading property of the blade spring can be made linear because the span of the blade spring can be maintained at a constant value and control of load becomes easier.
When the cross-section of the large diameter of the bushing is polygonal, both ends of the area of contact with the blade spring can be located more toward the edges of the blade spring end than the cut-out, so that the concentration of stress at the cut-out of the blade spring can be avoided under deformation of the blade spring.
For a further understanding of the present invention and the objects thereof, attention is directed to the drawings and the following brief description thereof, to the detailed description of the preferred embodiments of the invention and to the appended claims.